Infrared sensors are commonly used in the fields of science, business and military application. For example, an infrared sensor can serve as a laser detector, a missile guider, a remote controller, a burglary alarm and a thermal image detector, etc. Two major types are categorized for the infrared sensors, i.e. thermal electric type and quantum type. Compared with the other infrared sensors, the thermal electric type sensors have the following advantages:
1. They can be operated at room temperature, while the quantum type sensors have to be operated at a low temperature ranged within -100.degree. C. and -200.degree. C. for abating noises; and PA1 2. They respond even faster than that of Golay cells.
A conventional thermal electric type IR sensor possesses a capacitor structure or a metal/ferroelectric film/semiconductor field effect transistor (MFS-FET) structure. The thickness of the film cannot be too small (in general, greater than 2 .mu.m) for the purpose of preventing carriers from penetrating through the ferroelectric film. Such a sensor is called a thick film type IR sensor. The thick film type IR sensor has a thick ferroelectric film so that the heat capacity of the sensor is large, and the response time is long (longer than 40 .mu.s). In addition, when the intensity of the current converted from the infrared ray is smaller than e.g. 1 .mu.A, an additional amplifier will be required for switch operations and the response time will be further extended.